Transient Moisture Research Articles

Numerical Solution and it’s Analysis during Solar Drying of Green Peas

A mathematical model is developed for solar drying of green peas (Botanical name: Pisum Sativum). The problem is solved assuming the shape of the green peas is spherical. The governing transient mass transfer equation is discretized into finite difference scheme. The time marching is performed by implicit scheme. The governing equations and boundary conditions are non-dimensionalized to get generic results. The product in the chamber is in contact with air which is heated by solar energy, so the boundary conditions of third kind (convective boundary conditions) are considered. By space and time discretization a set of algebraic equations are generated and these algebraic equations are solved by tridiagonal matrix algorithm. A computer code is developed in MATLAB in order to compute the transient moisture content distribution inside the product. Center point, boundary and mean moisture of green peas are estimated at different temperatures and drying time. Present numerical result is compared with experimental result from literature and it was found that there is a good agreement of results. The drying time is predicted for how quickly the mean moisture of green peas is reached to 50, 40, 30, 20 and 10% of its initial moisture corresponding to different temperatures.

Atmospheric hydrological cycles in the Arctic and Antarctic during the past four decades

Atmospheric hydrological cycles over the Arctic and Antarctic have been investigated in the previous studies and there are some similarity and dissimilarity in the two polar regions. The Arctic and Antarctic are areas of moisture flux convergence through the year. So the precipitation (P) exceeds the evaporation (E) and the net precipitation (P-E) is positive. Therefore, the atmospheric moisture transport is a primary input of water into the polar regions. Meanwhile the climatological seasonal cycles of P-E over these regions are dominated by transient moisture flux associated with cyclone activities, the interannual variations are governed by the stationary flux associated with the Arctic Oscillation and the Antarctic Oscillation (AAO). In addition, recent climate changes influence the polar hydrological cycles. Our analyses using an atmospheric reanalysis up to recent years indicated that there were no significant long-term changes in the poleward moisture transport into both the Arctic and Antarctic during 1979-2016. On the other hand, the water vapor (precipitable water) were clearly increasing over the Arctic and gradually decreasing over the Antarctic during the same period. As expected, the increasing trend of water vapor was due to the large warming over the Arctic. There were two reasons for the gradually decreasing trend of water vapor over the Antarctic. The first one was the positive trend of AAO in summer and the second was deepening trend of the Amundsen low in autumn. The trends in water vapor and temperature during the past 38 years further suggest that both polar regions were getting dryer in several seasons. The trend, however, needs to be confirmed by follow-up climatological analyses.

Mathematical modelling of far-infrared vacuum drying processes

In this paper, a mathematical model of far-infrared vacuum drying of shrinkage body is presented. The system of two coupled partial differential equations for heat and mass transfer with appropriate initial and boundary conditions are solved numerically with used of the finite difference method. On the basis of the numerical solutions a computer program for calculation of temperature profiles, transient moisture content, mid-plane temperature, and the volume averaged moisture content changes for given drying regime was developed. For verification of the mathematical model a series of numerical drying experiments of potato slices were realized.

The influence of hygrothermal effects on the cross-ply composite laminate with transverse cracking in transient mode

The stiffness reduction of symmetric hygrothermal cracked and aged cross-ply laminates is predicted by using two different models, shear-lag and variational approach. The material properties are considered to be dependent on temperature and transient moisture distribution in desorption case. This transient hygrothermal effect is taken into account to access the changes in the longitudinal modulus due to transverse cracking. The obtained results illustrate well the dependence of the stiffness degradation on the cracks density and transient environmental conditions, especially at high temperature. Through the presented study, we hope to contribute to the understanding of hygrothermal behaviour of cracked composite laminate.

Prediction of Poisson's ratio degradation in hygrothermal aged and cracked [θm/90n]scomposite laminates

The Poisson ratio reduction of symmetric hygrothermal aged [θm/90n]s composite laminates containing a transverse cracking in mid-layer is predicted by using a modified shear-lag model. Good agreement is obtained by comparing the prediction models and experimental data published by Joffe et al. (2001). The material properties of the composite are affected by the variation of temperature and transient moisture concentration distribution in desorption case, and are based on a micro-mechanical model of laminates. The transient and non-uniform moisture concentration distribution give rise to the transient Poisson ratio reduction. The obtained results represent well the dependence of the Poisson ratio degradation on the cracks density, fibre orientation angle of the outer layers and transient environmental conditions. Through the presented study, we hope to contribute to the understanding of the hygrothermal behaviour of cracked composite laminate.

Theoretical modeling of water vapor transport in cellulose-based materials

The theory of mass transport in porous media is of fundamental importance for different applications such as food, paper packaging, textiles, and wood for building materials. In this study, a theoretical water vapor transport model has been developed for cellulose-based materials, such as paper and regenerated cellulose film. Pore diffusivities were determined from the dynamic moisture breakthrough experiments comprising a stack of paper sheets and regenerated cellulose films in a configuration similar to a packed adsorption column. Other mass transfer parameters were determined from transient moisture uptake rate measurements. The model incorporates pore and surface diffusion as a lump parameter into a variable effective diffusion coefficient. The mass transport, involving both pore and surface diffusions, is evaluated independently. The theoretical water vapor transmission rates (WVTRs) obtained from the model were compared with experimentally determined WVTRs measured under steady-state conditions. The theoretical model, based on intrinsic diffusion, stipulates higher WVTR values compared to the experimental results. However, the theoretical water vapor transfer rates agree well with the experimental results when external mass transfer resistance is incorporated in the model.

Experimental study and analysis of porous thin plate drying in a convection dryer

In this study experiments were conducted to study the porous thin plate drying process. An analysis was also carried out to determine the moisture transfer coefficients that vary with the moisture content of the plate during drying. The study is useful for analyzing the transient drying process of porous thin plates. Furthermore, energy and exergetic analyses based on the measured results were carried out to determine the dryer performance. It is found that, although the drying rate increases, the energy utilization ratio of the drying process decreases with either an increase in the rate of air flow or an increase in the size of the drying air inlet. The results indicate that a significant amount of the energy provided to the system was lost and not utilized for drying, especially for high drying rate dryers. An exergetic analysis showed that by adjusting the configuration of the air inlet and flow rate, the exergetic efficiency of the dryer can be significantly increased (from 0.5% to 10%). An overall transport phenomena analysis and performance evaluation including the transient moisture transfer coefficients, drying rate, energy utilization ratio, and exergetic efficiency in the current study provide comprehensive and important insights to the thermal physics of porous thin plate drying processes and the design of efficient dryer systems.

Responses of macropropagated <i>Musa</i> plantlets to transient moisture stress in six nursery substrates

Moisture stress causes serious devastating effects on crops ranging from retarded growth, tissue desiccation, and severe yield drop to outright death. In this study, the efficacy of six nursery substrates formulated in varying volume ratios of composted plantain fruit/bunch wastes (PFW), sawdust (SD), poultry manure (PM) and topsoil (TS) were evaluated on growth and moisture stress tolerance of macropropagated banana plantlets in the nursery. Un-amended topsoil was evaluated alongside five other substrates including PFW:SD (3:3), PFW:SD:PM (2:2:2), PFW:SD:PM:TS (1½:1½:1½:1½), SD:PM (3:3) and TS:PM (3:3) in a 6×2 factorial in completely randomized design (CRD) of ten replications. Two uniform sets of 10-week-old plants were used in the study. Watering was withdrawn on one set for 2 weeks, while the other set (watered daily throughout the study period) served as the control. The 2-week moisture stress was followed by a 4-week rehydration period, and thereafter, a second cycle water stress was induced for 3 weeks after which the plants were sampled for growth and dry matter accumulation. Results showed significant (p < 0.05) variability in plant growth and dry matter yield (DMY) across the nursery substrates, vis-à-vis the induced moisture stress. Plant growth and DMY were superior in PFW:SD:PM and PFW:SD:PM:TS, and were comparably good in most other media that contained PM and or PFW. The deleterious effects of the induced moisture stress were most severe in plants raised in un-amended topsoil. In addition to poor growth and reduced DMY observed in the stressed plants, these plants allotted a greater proportion of the accumulated dry matter to the underground components. It was evident from the study that inclusion of composted organic materials in nursery substrates supports the efficient utilization of available water by the plants. The use of organic substrates therefore holds promise for moisture stress management in nurseries. Irrigation (interval or volume) could be regulated to save labour, cut cost and optimize crop water use.Keywords: Nursery media, sucker plantlets, water stress, banana.

Insights into controls on hexavalent chromium in groundwater provided by environmental tracers, Sacramento Valley, California, USA

Environmental tracers are useful for determining groundwater age and recharge source, yet their application in studies of geogenic Cr(VI) in groundwater has been limited. Environmental tracer data from 166 wells located in the Sacramento Valley, northern California, were interpreted and compared to Cr concentrations to determine the origin and age of groundwater with elevated Cr(VI), and better understand where Cr(VI) becomes mobilized and how it evolves along flowpaths. In addition to major ion and trace element concentrations, the dataset includes δ18O, δ2H, 3H concentration, 14C activity (of dissolved inorganic C), δ13C, 3He/4He ratio, and noble gas concentrations (He, Ne, Ar, Kr, Xe). Noble gas recharge temperatures (NGTs) were computed, and age-related tracers were interpreted in combination to constrain the age distribution in samples and sort them into six different age categories spanning from <60yr old to >10,000yr old. Nearly all measured Cr is in the form of Cr(IV). Concentrations range from <1 to 46μgL−1, with 10% exceeding the state of California’s Cr(VI) maximum contaminant level of 10μgL−1. Two groups with elevated Cr(VI) (⩾5μgL−1) were identified. Group 1 samples are from the southern part of the valley and contain modern (<60yr old) water, have elevated NO3− concentrations (>3mgL−1), and commonly have δ18O values enriched relative to local precipitation. These samples likely contain irrigation water and are elevated due to accelerated mobilization of Cr(VI) in the unsaturated zone (UZ) in irrigated areas. Group 2 samples are from throughout the valley and typically contain water 1000–10,000yr old, have δ18O values consistent with local precipitation, and have unexpectedly warm NGTs. Chromium(VI) concentrations in Group 2 samples may be elevated for multiple reasons, but the hypothesis most consistent with all available data (notably, the warm NGTs) is a relatively long UZ residence time due to recharge through a deep UZ near the margin of the basin. A possible explanation for why Cr(VI) may be primarily mobilized in the UZ rather than farther along flowpaths in the oxic portion of the saturated zone is more dynamic cycling of Mn in the UZ due to transient moisture and redox conditions.

Effect of fibre topology on hygro-mechanical response of polymer matrix composites

Diffusion of moisture through fibre reinforced polymers (FRP) is one of the main environmental causes of their deterioration and loss of service life. Moisture diffusion and the resulting stresses in a fibre–matrix system vary considerably with the topology of the fibres inside the polymer matrix. This paper reports a numerical study on stress build up in FRP due to moisture diffusion. The Fickian diffusion model is implemented. Stresses due to the transient moisture distribution have been estimated using a finite element model. Some fundamental topologies have been studied. Most important topological parameters have been identified. Utilising the results of fibre neighbourhood, interpretation of large microstructures has been discussed. Considerable interactions among neighbouring fibres can be observed in the stress build up. The results should help in designing moisture impeding microstructures for FRP and prolong their life.

The Power Series as Water Sorption Isotherm Models

AbstractIn this study, a power series which can generate different families of new water sorption isotherm models were presented. Experimentally obtained values for equilibrium moisture content of pear for three different temperatures, 15, 30 and 45C, and water activities, from 0.112 to 0.920, as well as literature experimental values for equilibrium moisture content of potato for three different temperatures, 30, 45 and 60C, and water activities, from 0.112 to 0.900, were fitted with the newly generated sorption isotherm models plus the referent Anderson model known in the literature as Guggenheim‐Anderson‐de Boer (GAB) model. In order to find which model gives the best results for approximation of experimental sorption data, several statistical criteria proposed in scientific literature were used. For each model and experimental data set, the average performance index was calculated and models were ranked afterwards. After that, some statistical rejection criteria were checked (D’Agostino‐Pearson test of normality, single‐sample run test, confidence intervals of estimated parameters, significance and precision of the model parameters). The performed statistical analysis shows that the two newly generated three‐parameter models, M32 and M34, give the better fit to the sorption data of pear than the referent three‐parameter Anderson model, while M32 gives the best fit to the sorption data of potato.Practical ApplicationsThe sorption isotherms of food materials are of great importance in the food industry and technology, especially for the design and optimization of the drying equipment and in the approach to the prediction of shelf life stability of material. The new generated three‐parameter models, M32 and M34, can be successfully used in practical calculations of the equilibrium moisture content, which is an important parameter in storage conditions of dry food materials. With the incorporation of M32 or M34 in the drying model, more accurate values of transient moisture and temperature profiles on the dried materials will be obtained.

Hygro-thermo-mechanical Behavior of Adhesive-Based Flexible Chip-on-Flex Packaging

Although adhesive-based chip-on-flex (COF) packaging technologies have many advantageous features, such as flexibility and compatibility with standard semiconductor and microelectronics packaging processes, the low hygro-thermal resistance leads to reliability concerns. Thus, finite element (FE) modeling and experimental testing have been used to investigate the effects of temperature and humidity conditions on the hygro-thermo-mechanical behavior of a thin flexible anisotropic conductive adhesive (ACA)-based COF packaging technology. The investigation starts from process modeling of the thermo-mechanical behavior of the technology during the ACA bonding process. The validity of the process modeling is demonstrated by temperature and warpage experiments. Furthermore, three-dimensional (3-D) transient moisture diffusion FE analysis through a thermal–moisture analogy based on the “wetness” technique is performed to evaluate the moisture distribution, in which the moisture properties of the polyimide (PI) substrate are obtained through a moisture absorption experiment. Then, the effect of the moisture properties of the ACA adhesive and PI substrate on the moisture diffusion behavior is examined. Finally, following process modeling, 3-D hygro-thermo-mechanical FE analysis under a constant temperature and humidity condition is undertaken to assess the influence of hygro-thermal aging and stress relaxation of the ACA adhesive on the long-term contact performance of the interconnects.

Hygrothermal Effect in [θm/90n]s Cracked Composite Laminates – Desorption Case

Two analytical approaches were used to predict the effect of transverse cracks on the stiffness degradation, Shear-lag model and variational approach for [θm/90n]s composite laminates and under different environmental conditions by the variation of temperature and transient moisture concentration distribution in desorption case. Good agreement is obtained by comparing the prediction models and experimental data published by Joffe. Furthermore the cracked angle-ply laminate is submitted to hygrothermal conditions. The transient and non-uniform moisture concentration distribution gives rise to the transient relative reduction of the longitudinal Young's modulus. The obtained results represent well the dependence of the stiffness degradation on the cracks density, fibre orientation angle of the outer layers and transient hygrothermal conditions.

Mobile Observations of a Quasi-Frontal Transient Moisture Boundary in the Deep South

Abstract A protocol for the collection and analysis of high-resolution (≤300 m) temperature and humidity data along a transect using an unmodified passenger vehicle is described. A case is investigated of a weak dissipating cold front that became disconnected from its upper-tropospheric support and interacted with a developing Gulf of Mexico return flow. The changing relationships between the thermal and moisture gradients are described through cross-section analyses of the mobile, surface synoptic, and radiosonde data, extending from Texas to Alabama. The mobile transect data facilitated description of subsynoptic-scale airmass transition zones in the vicinity of the frontal remnant, as well as other variations within air masses. Similarities and differences are noted relative to previous studies of cold fronts, drylines, and coastal fronts.

Computational Modeling of Heat and Mass Transfer during Convection Cooking of Chicken Patties

A 2-D axisymmetric mathematical model base on Fourier’s equation and Fick’s law was developed to simulate coupled heat and mass transfer during convection cooking of chicken patties. The food physical properties were functions of local values of temperature and moisture content. The model equations has been solved by a commercial FEM package, called COMSOL Multiphysics. Transient temperature and moisture distributions inside the product were predicted, and a comparison between the theoretical predictions and experimental results reported in the literature has shown a good agreement. The developed model can be used to predict the cooking process.

Simulation of Osmotic Dehydration of a Spherical Material Using Parabolic and Power-Law Approximation Methods

In this article, one-dimensional transient moisture and solute diffusions in the spherical geometry during osmotic dehydration were modeled by exact analytical method and two approximate models. Approximate models have been developed based on a parabolic and power-law profile approximation for moisture and solute concentrations in the spatial direction. The proposed models were validated by experimental water loss and solid gain data obtained from osmotic dehydration of spherical cherry tomatoes in NaCl salt solution. Experiments were conducted at six combinations of two temperatures (30°C and 40°C) and three solution concentrations (10%, 18%, and 25% w/w). A two-parameter model was used to predict moisture loss and solute gain at equilibrium condition, and moisture and solute diffusivities were estimated by fitting the experimental moisture loss and solute gain data to the Fick's second law of diffusion. The values of mean relative errors for exact analytical, parabolic, and power-law approximation methods respect to the experimental data were estimated between 6.58% and 9.20%, 13.28% and 16.57%, and 5.39% and 7.60%, respectively. Although the parabolic approximation leads to simpler relations, the power-law approximation method results in higher accuracy of average concentrations over the whole domain of dehydration time.

Analysis of Transient Heat and Mass Transfer during Deep-Fat Frying of Pantoa

Pantoa is a traditional dairy product of the Indian subcontinent. Heat transfer in pantoa during deep-fat frying was evaluated using lumped thermal capacity model and one-dimensional transient heat conduction equation. Moisture and fat transfers were modeled using one-dimensional transient moisture diffusion equation and second order polynomial model, respectively. Lumped thermal capacity model was found to be unsuitable. As the frying temperature increased from 125C to 145C, the heat transfer coefficient obtained from one-dimensional transient heat conduction equation increased from 101.77 to 237.10 W/m2 K, while the moisture transfer coefficient increased from 7.79 × 10−6 to 9.05 × 10−6 m/s. The effective moisture diffusivity varied from 5.55 × 10−8 to 38.8 × 10−8m2/s for the temperature range studied. The moisture diffusivity was affected by frying temperature, and it was described by modified Arrhenius relationship. From the steady decline in Lewis number (2.18 to 0.35) with increase in frying temperature from 125C to 145C, it could be concluded that thermal diffusion was prominent at 125C, which was superseded by moisture diffusion at 145C. Practical Applications Pantoa is a traditional and popular dairy product of the Indian subcontinent. Deep-fat frying of pantoa involves simultaneous heat and mass transfer. In this study, the heat and mass transport during frying were analyzed and modeled. The effects of process temperature and time, on heat and mass transfer properties and diffusivities also were evaluated. The heat and mass transfer models will be useful to optimize the frying process and improve the quality of pantoa.

Modelling the internal stress field in argillaceous rocks under humidification/desiccation

SUMMARYThis paper deals with analytical and numerical modelling of the internal stress generated in argillaceous rocks during humidification/desiccation processes, which is an essential issue for damage study. This local stress field arises from two mechanisms: (i) complex interactions between free swelling/shrinking clay matrix and non‐strained inclusions of carbonate and quartz and (ii) a self‐restraint effect induced by the moisture gradient during the transient moisture exchange process. The inclusion–matrix interaction is investigated in different cases. Firstly, the analytical solution of the stress around a cylindrical inclusion embedded in an infinite swelling matrix is derived: The inclusion would suffer tension (compression) under humidification (desiccation), and the resulting cracking patterns are discussed. Then, the problem of two inclusions with different distances in an infinite swelling matrix is considered, and it is shown that the local stress around an inclusion will be perturbed and amplified by neighbouring inclusions. Finally, an inclusion outcropping at the free surface of a swelling matrix is modelled as to investigate the effect of free surface: The inclusion–matrix interface undergoes shear stresses of which the maximum is found at the free surface. In addition to the inclusion–matrix interaction, the self‐restraint effect is investigated: The induced stress is maximal at the beginning of humidification/desiccation processes and vanishes gradually with time. The quantity of the self‐restraint stress is strongly controlled by the hydric loading rate. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Numerical modeling of convective drying of food with spatially dependent transfer coefficient in a turbulent flow field

A numerical model is developed for prediction of transient moisture content of food materials. The moisture transfer is modeled considering diffusion of liquid water from inner layer to outer surface of the food material followed by evaporation of water from the surface to the dry air which flows over the moist food material. Discretization of transient heat and mass transfer governing equations are done using the finite-volume method (FVM). A 3-D code in MATLAB is developed to solve the simultaneous heat and mass transfer equations. The flow field over the moist food material is assumed to be turbulent and SST k–ω turbulence model is used for prediction of heat transfer coefficient using a computational fluid dynamics (CFD) commercial code. The sample moist food material is considered to be a rectangular shaped potato and the effects of temperature and velocity on drying behavior of the same are predicted. Different drying rate periods are identified. The numerical model is validated with experimental data with a reasonable agreement.

Dielectric frequency response of oil-paper composite insulation with transient moisture distribution

Because the temperature and load of transformer are variable, the moisture is usually inhomogeneous in oil-paper, especially for the traction transformer. In order to research the dielectric relaxation behavior of the oil-paper composite insulation with an inhomogeneous moisture distribution, it was proposed that a theoretical model for dielectric medium with an arbitrary distribution of conductivity and dielectric constant. The dielectric frequency response of oil-paper with transient moisture distribution was simulated by using the proposed model. The results show that transient moisture distribution caused the concentration polarization(CP), which enhanced the low-frequency relaxation. The model is validated against experimental data.